The principal aim of this study was to determine the incidence of Myocardial Infarction in the population aged 25-74 in Navarra, lethality after 28 days, and the characteristics of the treatment applied in the hospitals during the years 1997-1998. A search was conducted for possible cases of heart attack in the hospital services responsible for attending to them, by means of a review of clinical histories. The lethal cases that did not reach the hospitals were researched through the statistical bulletins of deaths, with the information on these deaths completed through the family doctors. 1,059 coronary events were registered, which corresponded to a crude rate of attack of 238 cases per 100,000 amongst men and 59 cases per 100,000 amongst women. Amongst the male patients who reached hospital alive, 50% were smokers, 41% showed hypercholesterolaemia, 35.9% were hypertense and 16% were diabetic. Amongst the women, who showed a higher average age, arterial hypertension was the most frequent risk factor, with 66%. During hospitalisation thrombolysis was carried out on 39.2% of the patients, primary or rescue angioplasty on 4.6%; aspirin or other anticoagulants were administered to 94.2%, beta-blockers to 60.6% and IECA to 37.4%. This study has shown that the frequency of Myocardial Infarction in Navarra is lower than that registered in many European and North American countries, and is concordant with the low rates of mortality due to this cause. Global analysis of the data shows that a high implementation of the care guidelines for this disease with respect to the use of efficient therapies could be observed in the years 1997 and 1998. Nonetheless, with the exception of the use of anticoagulants, hospital variability has been observed in the use of thrombolytic therapy and adjuvant therapies such as the beta-blockers or ACE Inhibitor, and in the use of diagnostic techniques such as arteriography.